In general, a thin film transistor includes a source electrode, a drain electrode, a gate electrode, a semiconductor layer, an insulating layer, and a substrate.
In general, ZnO is used as a channel material of the semiconductor layer, and specifically, Group 1 alkali (Li, Na) or Group 5 (N, P, As) is doped in ZnO to be used as a p-type channel material.
However, since ZnO may easily act as a hole killer that is spontaneously generated because a formation enthalpy of an oxygen vacancy, a Zn interstitial and the like capable of being acted as an n-type dopant is very low, it is difficult to perform the p-type doping as the semiconductor layer.
In addition, because an intrinsic characteristic of ZnO in which a formation enthalpy of an oxygen vacancy, a Zn interstitial and the like is low, in the case of when the ZnO thin film transistor is manufactured, there is an unstable state in that a strong n-type channel is formed and a threshold voltage and mobility of the channel are changed according to time.
Meanwhile, Korean Unexamined Patent Application Publication No. 2004-79516 discloses a method of forming a zinc oxide thin film in which a Group 5 element is added as a dopant on a substrate by using a zinc oxide compound including a Group 5 (N, P, As, Sb, Bi) element or oxides of a Group 5 element and activating the dopant. However, the method is disadvantageous in that the activation cannot be easily performed.
Therefore, in the case of when the ZnO thin film transistor is manufactured, since it is difficult to perform the p-type doping by using only the ZnO material, there is a need to develop a material that is capable of being used to perform the p-type doping by using Group 1 alkali (Li, Na and the like) or Group 5 (N, P, As and the like).